The fundamental objective of this research is to continue studies concerned with the biology of the mammalian lung surfactant system, emphasizing (but not exclusively) a variety of specialized preparative techniques which relate to electron microscopy. Of particular interest is the manner in which phospholipid is accumulated and stored in the secretory bodies of Type II pneumocytes. An approach well under way is to study appropriate phospholipid model systems that may stimulate the storage phase of surfactant material in these cells. Their physical state (phase) can be assessed by polarizing light microscopy, as well as by negatively-stained or shadowed preparations viewed by electron microscopy. The model systems can be manipulated by temperature. Model systems have been developed which have been prepared entirely under anhydrous conditions, to which water subsequently can be added and alterations followed. The effects of adding appropriate proteins so that proteolipid complexes may form can be examined. Type II cells also can be manipulated by temperature and the physical state of the stored phospholipid assessed by polarizing light microscopy. A variety of procedures which preserve and favor the retention of phospholipids in the preparation of ultrathin tissue sections for electron microscopy have been developed, and it is hoped that a correlation of these various approaches will provide clues as to the physical state of the surfactant materials in the secretory bodies of the Type II cells, as well as insights as to how the surfactant phospholipids may be dispersed to be ultimately rearranged and assembled with other substances (proteins and macromolecular carbohydrates)) after secretion into the alveolar spaces.